I’ve got a ‘classic’ single license for Sketchup 2018. The software is installed on my desktop computer and on my laptop. I have changed my laptop at least 2 or 3 times since the initial installation. However, the Sketchup license was never deactivated on it. This was twice not feasible due to a defect of the computer.
With the current new installation, I now get the message ‘This SketchUp Pro license has been used on too many computers’. A deactivation on the old computers is not possible, since these are long history.
Which version did you actually bought? Classic license included at least one year of maintenance and perhaps you did receive activation info for SketchUp 2019
(Although 2019 was released some 14 months later than 2018)
Search for license manager in the help pages to receive your latest version.
The easiest way is to subscribe to the latest and greatest in order to get support (you never need support until you need it, of course)